Migration Barriers Research Articles

Ion Concentration Gradient Induced Efficient Ion Migration in Hydrogen-Bonded Organic Frameworks for High-Performance, Self-Powered Humidity Sensing.

As one of the driving forces of ion migration, ion concentration gradients have large untapped potential to improve the performance of humidity sensors. A self-powered flexible humidity sensor based on hydrogen-bonded organic framework electrolytes wherein Na+ concentration gradients induce efficient ion migration is presented that can be attributed to the reversible effect of ambient water molecules on the migration barrier of Na+. The sensor exhibits superior flexibility, rapid responsiveness, high sensitivity (0.17 µA/% relative humidity), rapid response time (1.06 s), and outstanding stability (>200 cycles). The humidity-responsive device based on the Na+ concentration gradient exhibited excellent self-powering capability, eliminating the need for an external power unit and demonstrating impressive humidity power generation potential, which achieves a high current density of up to 164 mAm-2 and power density of 5.625 mWm-2. This research presents a new paradigm for developing self-powered humidity sensors and demonstrates their exceptional performance in noncontact sensing applications.

New fast ion conductors discovered through the structural characteristic involving isolated anions

One of the key materials in solid-state lithium batteries is fast ion conductors. However, Li+ ion transport in inorganic crystals involves complex factors, making it a mystery to find and design ion conductors with low migration barriers. In this work, a distinctive structural characteristic involving isolated anions has been discovered to enhance high ionic conductivity in crystals. It is an effective way to create a smooth energy potential landscape and construct local pathways for lithium ion migration. By adjusting the spacing and arrangement of the isolated anions, these local pathways can connect with each other, leading to high ion conductivity. By designing different space groups and local environments of the Se2− anions in the Li8SiSe6 composition, combined with the ion transport properties obtained from AIMD simulations, we define isolated anions and find that local environments with higher point group symmetry promotes the formation of cage-like local transport channels. Additionally, the appropriate distance between neighboring isolated anions can create coplanar connections between adjacent cage-like channels. Furthermore, different element types of isolated anions can be used to control the distribution of cage-like channels in the lattice. Based on the structural characteristic of isolated anions, we shortlisted compounds with isolated N3−, Cl−, I−, and S2− features from the crystal structure databases. The confirmation of ion transport in these structures validates the proposed design method of using isolated anions as structural features for fast ion conductors and leads to the discovery of several new fast ion conductor materials.

Gas-pressure-assisted strategy for precise control of palladium-based nanoparticle sizes: Unveiling size effects on methanol oxidation activity.

Gas-pressure-assisted strategy for precise control of palladium-based nanoparticle sizes: Unveiling size effects on methanol oxidation activity.

Genetic Monitoring of Brown Trout Released Into a Novel Environment: Establishment and Genetic Impact on Natural Populations.

Translocations are carried out either unintentionally or intentionally for conservation or management reasons. In both cases, translocated populations may genetically impact natural populations via introgression. Understanding how genetic background may affect an establishment in a novel environment and the potential risks for native populations is important for biodiversity conservation. Here, using a panel of 96 SNPs, we monitor the establishment of two genetically and ecologically distinct brown trout populations released into a mountain lake system in central Sweden where trout did not occur prior to the release. The release was carried out in 1979, and we monitor the establishment over the first three decades (5-6 generations) in seven lakes downstream of the release site. We find that extensive hybridization has occurred, and genes from both populations exist in all lakes examined. Genes from the population that was nonmigratory in its native environment have remained to a higher degree in the area close to the release site, while genes from the population that was more migratory in its native habitat have spread further downstream. All established populations exhibit higher levels of genetic diversity than the released populations. Natural, stream-resident brown trout populations occur ~15 km downstream of the release site and below a waterfall that acts as an upstream migration barrier. Released fish have spread genes to these populations but with low introgression rates of 3%-8%. Recently adopted indicators for monitoring genetic diversity were partly able to detect this introgression, emphasizing the usefulness of genetic indicators in management. The SNP panel used in this study provides a similar picture as previously used allozymes, showing that older marker systems with fewer loci may still be useful for describing the population structure.

Protons in (Ga,Sc,In,Y)3+-doped BaFeO3 triple conductors — Site energies and migration barriers investigated by density functional theory calculations

Protons in (Ga,Sc,In,Y)3+-doped BaFeO3 triple conductors — Site energies and migration barriers investigated by density functional theory calculations

Valence Engineering via Polyoxometalate-Induced on Vanadium Centers for Efficient Aqueous Zinc-Ion Batteries.

Layered vanadium-based compounds have attracted attention as cathode materials for aqueous zinc-ion batteries (AZIBs) because of their low cost, high theoretical specific capacity, and abundant vanadium valence states. However, the slow migration of Zn2+ ions and their poor cycling stability hinder their practical application in AZIBs. Herein, using a one pot solvothermal method, the polyoxometalates (POMs) were inserted into the aluminum vanadate interlayer spacing, and a series of novel three-dimensional nanoflower cathode materials (HAVO-MMo6-X) were successfully fabricated. The unique electron-rich structure of the POMs accelerated the migration of Zn2+ on the cathode to obtain a high specific capacity. Owing to the synergistic pillar effect of POMs and HAVO, the interlayer spacing of HAVO-FeMo6-50 increased to approximately 14.33 Å. X-ray absorption fine structure spectroscopy was used to analyze the coordination environments of the cathode materials. A combination of in situ and ex situ characterization techniques demonstrated the storage mechanism of Zn2+ during the charge/discharge process. Furthermore, the experimental results and DFT calculations indicated that the introduction of POMs had the dual function of improving conductivity and reducing the Zn2+ migration barrier. Thus, this work provides a new perspective on the synergistic interaction between POMs and metal compounds.

Valence Engineering via Polyoxometalate‐Induced on Vanadium Centers for Efficient Aqueous Zinc‐Ion Batteries

Layered vanadium‐based compounds have attracted attention as cathode materials for aqueous zinc‐ion batteries (AZIBs) because of their low cost, high theoretical specific capacity, and abundant vanadium valence states. However, the slow migration of Zn2+ ions and their poor cycling stability hinder their practical application in AZIBs. Herein, using a one pot solvothermal method, the polyoxometalates (POMs) were inserted into the aluminum vanadate interlayer spacing, and a series of novel three‐dimensional nanoflower cathode materials (HAVO‐MMo6‐X) were successfully fabricated. The unique electron‐rich structure of the POMs accelerated the migration of Zn2+ on the cathode to obtain a high specific capacity. Owing to the synergistic pillar effect of POMs and HAVO, the interlayer spacing of HAVO‐FeMo6‐50 increased to approximately 14.33 Å. X‐ray absorption fine structure spectroscopy was used to analyze the coordination environments of the cathode materials. A combination of in situ and ex situ characterization techniques demonstrated the storage mechanism of Zn2+ during the charge/discharge process. Furthermore, the experimental results and DFT calculations indicated that the introduction of POMs had the dual function of improving conductivity and reducing the Zn2+ migration barrier. Thus, this work provides a new perspective on the synergistic interaction between POMs and metal compounds.

Atomic‐scale oxidation mechanism of high‐entropy carbides via density functional theory and ab initio molecular dynamics

AbstractHigh‐entropy carbides (HECs) are increasingly recognized as promising materials for high‐temperature applications, thanks to their remarkable mechanical properties and resistance to oxidation. This study investigates the initial oxidation mechanisms of HEC (Zr₀.₂₅Hf₀.₂₅Nb₀.₂₅Ta₀.₂₅)C through density functional theory and ab initio molecular dynamics simulations. Our results indicate that the (100) surface exhibits the highest stability, where oxygen molecules dissociate into atoms that preferentially adsorb at the threefold hollow site. Further analysis shows that oxygen atoms preferentially bond with Zr and Hf atoms, leading to the formation of oxides. The interaction between oxygen and the surface exhibits mixed ionic–covalent characteristics. Furthermore, oxygen atoms diffuse from the surface to subsurface octahedral sites via tetrahedral interstitial sites, with a migration barrier slightly above that of corresponding binary carbides. This research enhances our understanding of the oxidation resistance in HECs.

Large-scale movement patterns of European catfish (Silurus glanis L.) in the Scheldt River basin, Belgium.

The large-scale movement behavior of European catfish (Silurus glanis L.) remains poorly understood, despite it being a species of interest for conservation management. We report the movement patterns of 13 native individual catfish, recorded using acoustic telemetry over 160-km estuarine habitat free of migration barriers in the Scheldt River basin (Belgium). The results show that catfish can travel vast distances of over 10 km with a seasonal pattern of fish moving the largest distances in summer. The wels catfish is often considered a relatively sedentary species; however, our results show that this is not the case in systems where they have the freedom to move over large distances. Knowledge about the large-scale movement behavior of the wels catfish can be useful for species conservation, as well as pest control. For instance, the effects of migration barriers could be (re)considered in terms of the large movement distances.

Rectified Water Migration Behavior in the Noncentrosymmetric Channels of a Ferroelectric Proton Conductor.

Ferroelectric ion conductors composed of noncentrosymmetric host structures and guest water molecules have recently garnered attention. These systems exhibit colossal polarization driven by long ion displacement facilitated by water molecules; however, the manner in which water molecules are perturbed by the polar backbone remains unclear. In this study, we investigated water migration behavior within the noncentrosymmetric channels of the ferroelectric proton conductor K2MnN(CN)4·H2O using various first-principles computational methods, including climbing image nudged elastic band (CI-NEB) calculations, potential energy surface (PES) scans, and ab initio molecular dynamics (AIMD) simulations. The energetic and dynamic characteristics governing water migration, obtained through CI-NEB and PES scans, revealed a significant directional preference for migration. Specifically, a lower activation barrier for migration in the negative c-axis direction compared to the positive one suggested rectification characteristics. These direction-dependent transition state energies were attributed to anisotropic arrangements of CN ligands, whose π orbitals interact with the highest occupied molecular orbital of the water molecule. In addition, AIMD simulations demonstrated that water molecules exhibit dynamically biased fluctuations around their equilibrium positions, corroborating the role of the polar framework as an internal electric field that directs water flow.

Recent Progress of Thin Crystal Engineering for Perovskite Solar Cells.

Metal halide perovskite single crystals hold promise for photovoltaics with high efficiency and stability due to their superior optoelectronic properties and weak bulk ion migration. The past several years have witnessed rapid development of single-crystal perovskite solar cells (PSCs) with efficiency rocketed from 6.5 % to 24.3 %, however, which still lags behind their polycrystalline counterparts. Moreover, the poor device stability under light illumination is contrary to the high ion migration barrier of perovskite single crystals. The key limiting factors should be the low crystalline quality and high surface defect density of solution-grown thin single crystals. Under this circumstance, a review paper summarizing the recent progress and challenges will be instructive for future development of this emerging field. In this manuscript, the crystal engineering used to enhance carrier transport and suppress carrier recombination in vertical single-crystal PSCs will be summarized initially, including crystal growth, component control, surface and interface modification. Subsequently, the application of perovskite single crystals in lateral single-crystal PSCs will be discussed and compared with the conventionally vertical structure. Finally, the challenges and proposed strategies for the development of single-crystal PSCs are provided.

Non-local interactions determine local structure and lithium diffusion in solid electrolytes

Solid-state batteries, in which solid electrolytes (SEs) replace their liquid alternatives, promise high energy density and safety. However, understanding the relation between SE composition and properties, stemming from intricate interactions among constituent sublattices that involve non-local electronic and nuclear dynamics, remains a critical and unsolved challenge. Here, we evaluate electronic structure methods and demonstrate that a density-functional approach incorporating non-local and many-body effects in exchange-correlation interactions provides predictive results for the local structure and diffusion properties of SEs. Focusing on argyrodite SEs (Li6±xM1±yS5±zXn, LMSX; M = P, Ge, Si, Sn; X = Cl, Br, I), we explore their compositional landscape as a test case. The employed HSE06+MBDNL method unveils how the S/X site disorder dictates the diffusion of lithium by controlling the number and length of the diffusion pathways. Additionally, non-local exchange and van der Waals interactions precisely modulate the coupling between the framework lattice and mobile lithium ions, thereby influencing the migration barrier. Consequently, the interplay of non-local electronic interactions in the predictive design of Li-solid electrolytes – and likely many other functional materials – is emphasized.

Hydrogen Diffusion in Ti3C2 MXenes.

For energy storage in 2D MXenes using hydrogen, it is crucial to understand the relevant diffusion mechanisms. Density functional theory was used to determine hydrogen migration barriers, hopping frequencies, enthalpy and entropy of vacancy formation, and the diffusion coefficient of various possible migration paths. The results show that H diffusion is primarily governed by interstitial diffusion. For all investigated diffusion paths, the diffusion coefficients and prefactors, D0, the corresponding activation energy, E, and the hopping frequencies are calculated from the ab initio approach.

MD assessment of irradiation resistance of FeMnNiCr under successive bombardment

Abstract The irradiation resistance behavior of Co-free high-entropy alloy FeMnNiCr under successive bombardment is investigated by means of molecular dynamics simulations. There are much less residual defects in FeMnNiCr referring to Ni after prolonged irradiation and large-size defect clusters are observed in FCC Ni but not FeMnNiCr. The formation and growth of dislocations in FeMnNiCr are significantly suppressed. The migration barriers of interstitials are similar to these of vacancies in FeMnNiCr, resulting in a higher efficiency of defect recombination. The defects in Co-free FeMnNiCr show similar trends with NiCoCrFeMn and NiCoCrFe during the irradiation process, suggesting its good potential in nuclear structure materials applications.

The Role of Ion-Polaron Electrostatic Attraction on Zn2+ Migration in α-V2O5 for Zinc Ion Battery: Insights from First-Principles Calculations.

The migration of Zn2+ ions is significantly more challenging compared to that of Li+ ions within the same crystalline framework, leading to poor rate performance of zinc-ion batteries (ZIBs). Compared to Li+, the slower migration rate of Zn2+ is vaguely attributed to the stronger electrostatic interaction induced by Zn2+. Herein, the rule of how the size of the migration channel and electrostatic interaction affect Zn2+ and Li+ migration in α-V2O5 has been systematically investigated by first-principle calculations. It is found that expanding the layer spacing can facilitate Zn2+ migration. Once the layer spacing surpasses a certain threshold, further expansion does not lead to a continued reduction in the migration barrier. The local structure distortions caused by electron small polarons would lead to a decrease in migration channel size, which should have increased the energy barrier for Li+ and Zn2+ migration. However, interestingly, the electron small polarons decrease the energy barriers, which would be attributed to the ion-polaron electrostatic attraction. The higher activation barriers for the migration of Zn2+ ions compared to those of Li+ ions can be rationalized by the specific ion-polaron electrostatic attraction for Zn2+. Moreover, the comparative strength of the polaron-ion electrostatic attraction for alkali and alkaline earth metal ions is unveiled. Overall, this study provides theoretical insights into the role of ion-polaron electrostatic attraction on ion migration.

Composition-Dependent Voltage-Driven OFF-ON Switching of Ferromagnetism in Co-Ni Oxide Microdisks.

Magneto-ionics, which refers to the modification of the magnetic properties of materials through electric-field-induced ion migration, is emerging as one of the most promising methods to develop nonvolatile energy-efficient memory and spintronic and magnetoelectric devices. Herein, the controlled generation of ferromagnetism from paramagnetic Co-Ni oxide patterned microdisks (prepared upon thermal oxidation of metallic microdisks with dissimilar Co-Ni ratios, i.e., Ni25Co75 and Ni50Co50) is demonstrated under the action of voltage. The effect is related to the partial reduction of the oxide phases to their metallic forms. Samples richer in Co show stronger magneto-ionic activity, which manifests in lower-onset threshold voltages, faster switching rates, and larger values of the attained saturation magnetization. By means of scanning electron microscopy, a cobalt segregation phenomenon has been experimentally observed upon thermal oxidation, which has been theoretically discussed from the diffusivities' viewpoint. X-ray diffraction characterization has revealed transitions between purely mixed Ni and Co oxides, in the OFF state, to a mixture of oxide and metallic phases, in the ON state, because of the oxygen ion motion outward/inward the Co-Ni oxide microdisks, depending on the voltage polarity. Ab initio calculations reveal that the energy barrier for oxygen vacancy migration is lower in CoO than in NiO, in agreement with the obtained magneto-ionic responses. The observation of magneto-ionic effects in patterned disks (and not only in archetypical continuous films) is a step further for the practical utilization of this phenomenon in real miniaturized devices.

Locking Pd Nanoparticles in N-Doped Carbon Derived from Conjugated Microporous Polymer for Stable Lithium Metal Anodes.

The uncontrollable growth of Li dendrites and large volume change during cycling limit the practical applications of Li metal anodes. Herein, the in situ-formed Pd nanoparticles locked in three-dimensional N-doped microporous carbon (Pd/NMC), which are derived from the catalyst for Buchwald-Hartwig (B-H) coupling polymerization, have been constructed to address these issues. The homogeneously distributed Pd nanoparticles effectively reduce the overpotential of Li nucleation through the reversible Li-Pd alloying reaction and boost Li+ diffusion by reducing the migration barrier. Furthermore, the Pd nanoparticles guide the Li selective nucleation and uniform growth in the 3D N-doped microporous carbon. Meanwhile, the spatial confinement effect alleviates the volume changes. As a result, the stable and reversible Li metal anode exhibits a high Coulombic efficiency of 98.7% over 1000 cycles at 1 mA cm-2. Full cells with LiFePO4 (LFP) as the cathode deliver a long lifespan of 600 cycles with 0.02% capacity decay per cycle at 2 C. This work provides a new polymerization-carbonization strategy to prepare a lithiophilic host for energy-dense Li metal batteries.

Effect of microstructure and neutron irradiation defects on deuterium retention in SiC

Retention of hydrogen isotopes is a critical concern for operating fusion reactors as retained tritium both activates components and removes scarce fuel from the fuel cycle. Radiation-induced displacement damage in SiC influences the retention of hydrogen isotopes compared to pristine SiC. Deuterium retention in neutron irradiated high purity SiC has been compared to different microstructures of non-irradiated high purity SiC using thermal desorption spectroscopy after gas charging and low energy ion implantation. Experimental results show lower deuterium retention in single crystal SiC than in polycrystal SiC indicating that grain boundaries are key trapping features in unirradiated SiC. Deuterium is released at lower temperatures in neutron irradiated polycrystal SiC compared to pristine polycrystal SiC, suggesting weaker trapping by radiation-induced defects compared to grain boundary trapping sites in the pristine materials. Low energy ion implantation caused a high deuterium release temperature, highlighting the sensitivity of deuterium release behaviour to radiation defect characteristics. First principles calculations have been conducted to identify energetically favourable trapping sites in SiC at the HABcVSi and HTSiVC complexes, and migration barriers between interstitial sites. This helps interpret experimental results and derive effective diffusivity of hydrogen isotopes in SiC in the presence of vacancies.

Unraveling the Mechanisms of Lithium-Alloy Plating in Ag-C Anode: In situ SEM Study.

The Ag-C composite anodes facilitate stable LixAg deposition in solid-state batteries. However, the role of carbon and the kinetics of lithium migration and deposition in the composite structure remain unclear. Few studies have focused on this critical research area owing to a shortage of effective, non-destructive characterization methods that can directly observe the Li alloy deposition process in solid-state batteries in real time. In this study, Li alloy formation on the Ag-C anode is investigated through operando X-ray diffraction (XRD) analysis and scanning electron microscopy combined with in situ probing. This enables the observation of the composition and morphology of the LixAg alloy as it evolves within the Ag-C composite anode during discharge. Further insights from scanning transmission electron microscopy-electron energy loss spectroscopy and first-principles simulations on lithiophilicity and the energy barrier for lithium migration reveal a complex lithium migration and deposition mechanism within the Ag-C anode.

Regulating Chemical Bonds in Halide Frameworks for Lithium Superionic Conductors.

Developing solid-state electrolytes (SSEs) is a critical task for advancing all-solid-state batteries (ASSBs) that promise a high energy density and improved safety. The dominant strategy in engineering advanced SSEs has been substitutional doping, where foreign atoms are introduced into the atomic lattice of a host material to enhance ionic conduction. This enhancement is typically attributed to optimized charge carriers' concentration or lattice structure alterations. In this study, we extend the concept of substitutional doping to explore its effects on chemical bond modulation and the resulting impact on ionic conduction in halide SSEs. As a case of study, we demonstrate that cation dopants with high charge density indices (e.g., Al3+ and Fe3+) can increase the covalency of metal-halide (M-X) bonds and induce the local asymmetric field of force, resulting in higher site energy and lower migration barriers, which significantly enhance the ionic conduction in halide frameworks. Specifically, we developed a series of halide SSEs with ionic conductivities exceeding the benchmark value of 1 mS cm-1 at room temperature. Detailed investigations, including neutron powder diffraction, pair distribution function analysis, and first-principles calculations, are performed to gain an insight into the mechanisms behind this adjustment. Furthermore, these materials exhibit enhanced deformability due to increased covalency of the metal halide framework, enabling high-performance ASSB prototypes operatable at low stacking pressures (<10 MPa). These advancements deepen our understanding of superionic conduction in halide SSEs and mark an important step toward the practical application of ASSBs in the future.